2026 Air Quality Look Ahead

While 2025 brought a new administration and changes to how the United States Environmental Protection Agency (U.S. EPA) approaches air quality regulation and policy, we expect to see even more air quality regulatory activity in 2026. The Spring 2025 regulatory agenda was already outdated by the time it was released in Fall 2025, the government shutdown delayed several actions, and no Fall 2025 regulatory agenda was issued. However, we can speculate on actions that are likely to occur in 2026 based on 2025 executive orders and other announcements from the administration, which consistently emphasize energy from fossil fuel, new data centers, and reducing regulatory and permitting burden.

New Source Review

In 2025, we saw three important New Source Review (NSR) guidance changes and a withdrawal of the 2024 proposed revisions to the NSR rule. In 2026, we should see a rulemaking related to the definition of “Begin Actual Construction.” Air quality regulations prohibit beginning actual construction of a major stationary source prior to obtaining an air permit. State and federal air quality regulations characterize “begin actual construction” as “the initiation of physical on-site construction activities on an emissions unit, which are of permanent nature….” Previous U.S. EPA guidance had precluded construction of ancillary buildings or structures, even if they were not emissions units. With the 2025 determination, U.S. EPA states that “begin actual construction” does not apply to the parts of a facility that do not qualify as an emissions unit and that previous guidance (i.e., the March 28, 1986 Reich memo) adopted an overly broad reading of the term. This change is important because it potentially shrinks a Prevention of Significant Deterioration (PSD) project’s construction timeline by allowing several significant construction activities to be performed prior to permit issuance.

The Spring 2025 regulatory agenda indicates that U.S. EPA is planning a rulemaking around minor NSR and public participation. The previous administration requested comments on what changes it should require in state minor NSR programs over concerns that included a lack of public participation included in certain permitting mechanisms (e.g., permits by rule). It will be important to monitor whether this item remains on the next regulatory agenda because it would add burden and time to certain permitting mechanisms for small changes at facilities.

On the subject of NSR guidance, industry associations have communicated to U.S. EPA their desires around what guidance should be rescinded and what additional guidance should be developed. We may see new guidance around routine maintenance, repair, and replacement; netting; or demand growth and we could see additional guidance that conflicts with current policy or regulatory interpretations rescinded. All signs point to a regulatory environment that is favorable to NSR permitting. If you are considering a capital project at your facility, 2026 might be the best time to get it permitted.

National Ambient Air Quality Standards

The biggest question around the National Ambient Air Quality Standards (NAAQS) in 2026 will be whether designations are made for the recently revised annual fine particulate (PM_2.5) NAAQS of 9 micrograms per cubic meter (µg/m³⁾ or if the court rescinds that NAAQS based on pending litigation over whether U.S. EPA can revise a NAAQS through a reconsideration. Regardless, U.S. EPA is behind on its five-year reviews of most NAAQS, and currently has no Clean Air Scientific Advisory Committee (CASAC) to inform its review process, so it is uncertain how much progress will be made on these reviews this year. The new administration could implement a more streamlined NAAQS review process in an effort to actually complete a review in five years. In 2026, we should see changes around the exceptional events policy (to make it easier for states to exclude certain events that cause elevated ambient impacts and avoid nonattainment), and we expect proposed revisions to the 2023 Good Neighbor Plan (which is currently stayed) and approvals of many of the previously rejected State implementation plans (SIP) that prompted the last administration to develop the Plan. Industry associations have advocated for changes to the Appendix W modeling guidelines or to guidance to reduce conservatism inherent to air dispersion modeling, but it remains to be seen whether U.S. EPA has the resources to make the desired changes or if it is willing to do so.

Maximum Achievable Control Technology Rules and New Source Performance Standards

The previous U.S. EPA administration revised several Maximum Achievable Control Technology (MACT) rules to fill perceived gaps in the pollutants and sources regulated. This administration seems to be taking a different view of when it is necessary to gap fill and what tools can be used. The Congressional Review Act (CRA) was used to eliminate the previous administration’s revisions to the Rubber Tire Manufacturing MACT and the provisions around source reclassification. 2025 saw proposals that considered whether it was not necessary to regulate some hazardous air pollutants (HAP) or sources of HAP because emissions were de minimis or did not pose risk. Several facilities subject to revised standards in various sectors also received a Presidential compliance extension. We expect U.S. EPA to propose changes to many of the MACT rules that were revised in the last administration (e.g., chemicals, lime manufacturing, iron and steel, etc.) and finalize MACT rule revisions for sectors such as wood products, hazardous waste combustors, secondary lead smelting, power, and chemicals. Stay tuned for lookahead articles on the forest products, power, and chemical sectors that will have more details.

U.S. EPA also recently proposed to delist 2-butoxyethyl benzoate and streamline the delisting process by removing the opportunity for public comment on whether a delisting petition is complete. Rather than issuing a Federal Register notice when it receives a complete petition, U.S. EPA proposes to inform the petitioner, complete its review, and then propose to grant or deny the petition.

On the New Source Performance Standards (NSPS) front, U.S. EPA is expected to finalize decisions around whether and how to regulate greenhouse gas emissions from utility boilers and combustion turbines in early 2026 and just recently finalized its review of the combustion turbine NSPS Subpart KKKK. The final revised combustion turbine standards for nitrogen oxides (NOx) in Subpart KKKKa are generally less stringent than proposed. U.S. EPA will also issue a proposed reconsideration on certain items in the 2024 revised chemical sector NSPS.

Regional Haze

The goal of the regional haze rule (RHR) is for states to achieve natural visibility conditions in Class I areas by 2064. SIP are required every 10 years to implement actions that achieve reasonable progress toward that goal. Many other air quality regulatory programs, both federal and state, have reduced emissions of haze-forming pollutants such that states have been making progress without having to include much in their regional haze SIP. However, the current regulatory language and U.S. EPA guidance still requires states to analyze sources and select a subset for a four-factor analysis to determine if additional emissions controls should be required. States took different approaches for the most recent review, but the process can be resource intensive for both industry and regulators. U.S. EPA is in the process of revising the rule to incorporate additional flexibility and reduce or eliminate review requirements during a 10-year review period if a state is well below the “glide path” to natural conditions. The deadline for SIP addressing the next planning period was recently extended from July 31, 2028 to July 31, 2031 while the rule is revised. We saw a request for comments in October 2025 to inform the regulatory update process and we should see proposed changes to the regional haze rule in 2026. The rule could set a threshold for determining whether a state has to consider additional reductions to make reasonable progress toward the 2064 goal, or a threshold at which a source’s contribution to regional haze is de minimis and no analysis for additional controls is required. More deference is expected to be given to states to decide what improvements are needed and what controls are cost effective.

Conclusion

With any of the changes on the horizon, there is likely to be litigation, so it will take time to see what regulatory updates are permanent. ALL4 has a large and experienced air quality consulting practice and we continuously monitor federal and state air regulatory developments. We can help you comment on regulatory proposals and draft policies, evaluate how regulatory changes could affect your facility, strategize on how to implement new regulations or permit projects, permit changes to your facility, implement new regulations and permit requirements, and track ongoing compliance with requirements. Please reach out to your ALL4 project manager or Amy Marshall with any question or if you need air quality consulting support.

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